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NOT_FIXED_DEC

林塬 2023-06-15 阅读 42


#define NOT_FIXED_DEC 31

为什么要定义成31,而不是用一个其他的值表示呢?比如,-1

通过做Round函数,明白了背后的一种设计初衷:因为广义的scale可以为负数。如下例:

mysql> SELECT round(333.33, -1), round(333.33, 1);
Field   1:  `round(333.33, -1)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       NEWDECIMAL
Collation:  binary (63)
Length:     5
Max_length: 3
Decimals:   0
Flags:      NOT_NULL BINARY NUM

Field   2:  `round(333.33, 1)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       NEWDECIMAL
Collation:  binary (63)
Length:     7
Max_length: 5
Decimals:   1
Flags:      NOT_NULL BINARY NUM


+-------------------+------------------+
| round(333.33, -1) | round(333.33, 1) |
+-------------------+------------------+
|               330 |            333.3 |
+-------------------+------------------+
1 row in set (0.00 sec)

如果NOT_FIXED_DEC用-1表示,则会和这种广义Scale相冲突。用31表示,则可以避开有效值域。


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